This application is based on French Patent Application No. 00 13 512 filed Oct. 23, 2000, the disclosure of which is hereby incorporated by reference thereto in its entirety, and the priority of which is hereby claimed under 35 U.S.C. xc2xa7119.
1. Field of the Invention
The invention relates to a method, an arrangement and interface system for charging electrical batteries that supply voltages of the same order and which are composed of rechargeable cells which can be of different kinds from one battery to another. It uses a charger device able to supply at least one constant regulation voltage suitable for a battery. It aims to protect the cells of a battery against overvoltages likely to occur during charging.
The arrangement envisaged is of the type which temporarily substitutes a battery for another power supply to power a load circuit if that other supply is temporarily unable to do so. The previously charged battery remains on permanent xe2x80x9cfloatingxe2x80x9d charge, for example, if the other supply is operating. This kind of arrangement routinely combines a battery, a device for charging the battery from a supply, and a load circuit, all of which are permanently interconnected. This configuration is used with telecommunication equipment that is intended to operate without interruption, for example.
The arrangement can also be organized differently, so that the battery, which can power a load circuit, can be charged intermittently from a supply via a charger device. The latter can top up the charge, using the technique referred to above, when the supply is operating. This is the case, for example, if the battery is that of an arrangement including a charger device that is powered by a supply rendered active on demand and/or as and when required, as in an electric vehicle. Descrirtion of the prior art Arrangements of the above kind are routinely equipped with means for balancing the various rechargeable cells that constitute a battery, for optimum management over time. Such means are disclosed by European patent 121 547, among others.
There are many devices for charging a battery which supply a predetermined regulation voltage. There are also many devices providing the facility to select one or more of a number of regulation voltages, in particular for charging different batteries.
Because of the standardization of rechargeable batteries and non-rechargeable dry cells, it is often possible to power the same equipment, by supplying it with a sufficient voltage for it to operate, by means of a battery, that is to say a particular system of cells of the same kind, rechargeable or not, chosen from a range of systems, as a function of the requirements of the user and/or what is available in terms of batteries at the time in question. The battery cells that can be substituted for each other are lead-acid cells, alkaline cells and lithium cells, for example.
However, to be really advantageous, this substitution facility implies that users can charge at least some of the different kinds of batteries using the same device, rather than using individual devices each suitable for a different battery. The necessity to have different charger devices has undoubted drawbacks for users wishing to be able to use batteries of different kinds, in place of each other, as a function of what they require or what is available at the time, to power the same load circuit in the context of a particular arrangement.
The skilled person knows that the overvoltages likely to occur during charging can have a harmful effect on the battery cells subjected to them, especially if the cells are more sensitive to overvoltages than other kinds of cell, as is the case with lithium cells, for example.
It is therefore necessary to take precautions if it is intended to charge a battery using a device designed for another battery, based on the fact that the battery has substantially the same nominal voltage.
The skilled person knows that a voltage step-up/step-down unit can be added to the electrical circuit connecting a charger device to a battery if the latter is supervised by a management circuit which transmits a control signal to the voltage step-up/step-down unit to modify the voltage supplied to the battery. The unit reduces the voltage when a battery cell is overcharged. However, this kind of additional component is costly and may be a problem if no space is provided for it on the battery or the charger device.
The skilled person also knows that a charger device, for example an individual charger of the usual kind for lead-acid batteries, can be used to charge batteries of a different kind if it is possible to modify the regulation voltage supplied by the device to prevent all risk of overvoltage at each of the cells of the battery being charged.
There are charger devices designed to receive an analog regulation voltage control signal. However, this kind of charger device can be used only with a battery to be charged which is associated with an interface providing an appropriate analog control signal. This kind of interface has drawbacks that correspond to those of an additional voltage step-up/step-down unit and requires a power supply to meet its requirements.
In some arrangements in which a battery is used in association with a charger device, there is also provided a circuit connected in parallel with each rechargeable cell to divert at least some of the current that is supplied to the battery by the charger device and which flows in that cell if the voltage measured at the terminals of the cell by an associated measuring circuit exceeds a particular threshold value.
An arrangement of this kind is specifically disclosed in European patent 121 547, referred to above. Its components can be physically associated in modular form with the rechargeable battery cell to which they are assigned, or possibly a group of such cells, in an autonomous hardware unit. This kind of unit can be connected in series with at least one other identical autonomous unit to form a battery in which balancing is ensured cell by cell.
The invention proposes a method of charging an electrical battery by means of a charger device able to supply at least one appropriate constant regulation voltage to the battery to be charged, regardless of the nature of the rechargeable cells constituting the battery, provided that the battery has a nominal voltage compatible with the regulation voltage or voltages that the charger device supplies, the method including the following steps:
continuously measuring the voltage at terminals of each rechargeable cell of the battery;
activating an associated individual shunt circuit connected in parallel with each rechargeable cell as soon as the voltage measured at the terminals of the rechargeable cell exceeds a particular regulation minimum threshold value fixed as a function of the nature of the rechargeable cell and for as long as the measured voltage is above the minimum threshold value;
supplying an indication as to whether a balancing maximum threshold value fixed as a function of the nature of a rechargeable cell is exceeded or not by the voltage measured at the terminals of the rechargeable cell;
translating into the form of a single binary signal respective indications as to whether the maximum threshold is exceeded or not obtained for each of the rechargeable cells at a given time, the single signal being maintained at a first binary value for as long as none of the voltages measured at the terminals of the rechargeable cells of the battery exceeds the maximum threshold value and at a second value otherwise; and
translating the single signal obtained from the indications as to whether the maximum threshold is exceeded or not into a signal controlling switching of a battery charging characteristic between two characteristics that can be selected either directly at the charger device or via an auxiliary device associated therewith.
The invention also proposes an arrangement including a battery made up of rechargeable cells connected in series and a charger device able to provide at least one constant regulation voltage for charging the battery, which is associated with:
an individual interface for each rechargeable cell of the battery, including a first voltage measuring circuit connected to terminals of the rechargeable cell concerned to control a current shunt circuit connected in parallel with it in order to shunt at least some of the charging current that is supplied to it if the voltage measured at the terminals of the rechargeable cell exceeds a particular regulation minimum threshold value fixed as a function of the nature of the cell, the individual battery interfaces each including a second voltage measuring circuit for determining if a balancing maximum , threshold value is exceeded at the terminals of the associated rechargeable cell to which the individual interface is assigned, on the basis of a voltage measured across a measuring resistor in series with the shunt device of the interface between the terminals of the associated rechargeable cell, and a circuit constituting a transmission AND logic gate which transmits a binary indication as to whether the balancing maximum threshold value is exceeded or not at the terminals of the associated rechargeable cell;
a common interface to which the individual interfaces are connected and to which each supplies at least one indication of the measured voltage for the associated rechargeable cell, the indication being used to control charging by the charger device, the common interface translating any indication relating to the balancing maximum threshold value being exceeded supplied to it by means of a transmission chain into which the transmission gates of the individual interfaces are inserted in series in the form of a charge characteristic switching control signal; and
a charger device which has at least one battery charge characteristic which is modified either in the charger device itself or in an associated-auxiliary device as a function of the characteristic switching control signal.
The invention further proposes an interface system for a battery made up of rechargeable cells, which system includes:
an individual interface for each rechargeable battery cell, each individual interface including a voltage measuring circuit connected to terminals of one of the rechargeable cells to control a current shunt circuit connected in parallel with the cell in order to shunt at least some of the charging current applied to it if the voltage measured at the terminals of the cell exceeds a particular regulation minimum threshold value fixed as a function of the nature of the cell, the individual battery interfaces each including a second voltage measuring circuit for determining if a balancing maximum threshold value is exceeded at the terminals of the associated rechargeable cell, to which the individual interface is assigned, on the basis of a voltage measured across a measuring resistor in series with the shunt device of the interface between the terminals of the associated rechargeable cell, and a circuit constituting a transmission logic AND gate which transmits a binary indication as to whether the balancing maximum threshold value is exceeded or not at the terminals of the associated rechargeable cell; and
a common interface to which the individual interfaces are connected for each to supply at least one indication relating to the voltage measured for the associated rechargeable cell, the indications being used by a charger device to control charging, the common interface translating any indication relating to the balancing maximum threshold value being exceeded, supplied to it by means of a transmission chain into which the transmission gates of the individual interfaces are inserted in series, in the form of a charge characteristic switching control signal for use by a charger device either directly or via an associated auxiliary device.
The invention, its features and its advantages are explained in the following description, which is given with reference to the single figure of the accompanying drawing.